1. Field of the Invention
The present invention relates to a channel reservation control system, an originator-side channel reservation controller, a recipient-side channel reservation controller, and a method of controlling channel reservation. More particularly, the present invention relates to the following technical fields: a channel reservation control system which controls reservation of data channels in Integrated Services Digital Network (ISDN) facilities interconnecting electronic switching systems; an originator-side channel reservation controller which controls data channel reservation on the side of a calling party; a recipient-side channel reservation controller which controls data channel reservation on the side of a called party; and a method of controlling data channel reservation.
2. Description of the Related Art
Automatic Call Distribution (ACD) systems have been introduced to many organizations to efficiently handle incoming calls from their customers in telemarketing, customer services, or other phone intensive business functions. When incoming calls arrive, an electronic switching system with ACD capabilities automatically greets the callers and queues them for available service reception terminals.
FIG. 17 shows an example of such an ACD service system. Private Branch Exchanges (PBXs) 100, 110, and 120 are linked to different portions (N1, N2, and N3) of a public switched telephone network (PSTN) through PSTN transmission lines 200 as indicated by the broken lines. These PBXs 100, 110, and 120 are also linked with each other through ISDN transmission lines 30 as indicated by bold solid lines. Service reception terminals are divided into three ACD groups Gr100, Gr110, and Gr120 under the control of their local PBXs 100, 110, and 120, respectively. The first ACD group Gr100 consists of a plurality of service reception terminals 100a to 100d. Likewise, the second ACD group Gr110 consists of terminals 110a to 110d, and the third ACD group Gr120 includes terminals 120a to 120d. 
The PBX 100, for instance, receives incoming calls addressed to its local ACD group Gr100, and it automatically delivers them to available service reception terminals being selected from among the service reception terminals 100a to 100d, thereby distributing the service workloads. When none of the service reception terminals 100a to 100d is found idle, the PBX 100 transfers the calls to other ACD Groups Gr110 and/or Gr120, so that the workloads will be distributed over the plurality of ACD groups and the incoming calls can be efficiently handled, not annoying the customers with busy signals.
As described above, the PBXs have to interact with each other to provide necessary information about the calling customer every time an incoming call is processed. This requirement justifies the use of ISDN transmission lines for connection between PBXs. Consider a call transfer from PBX 100 to PBX 110 via the ISDN transmission line 30a, for example. When setting up the call, the PBX 100 located on the side of the call originator first finds and obtains an idle data channel on an ISDN transmission line 30a interconnecting the PBXs 100 and 110. The PBX 100 then notifies the remote PBX 110 about the data channel obtained, and in response to this notification, the PBX 110 makes a hunting of the same data channel. In this way, the two PBXs 100 and 110 establish a call connection after negotiating which data channel to use.
In normal situations, the ISDN transmission line 30a is shared by a plurality of general subscribers for a variety of service purposes, but not dedicated to the ACD call transfer. Therefore, it may not always be possible for the PBXs 100 and 110 to obtain a data channel and set up a call connection, when there is a large volume of traffic between them. In such circumstances, the PBXs are unable to provide satisfactory ACD services.
Imagine another situation where the PBX 100 has obtained an idle data channel, but unfortunately, that data channel is not operational on the side of the PBX 110. This can happen when, for example, one electronic switching system (i.e., PBX) is under the maintenance activities and thus some of its data channels are unusable. In this case, the ACD service does not work, because no call connections can be established between the PBXs 100 and 110. Such problem situations could be avoided by allocating a wider bandwidth to the ISDN transmission line 30a between the PBXs 100 and 110 so that the expected volume of incoming calls be handled. This solution, however, would result in an intolerable increase in system costs.
Researchers have proposed several ideas to avoid the above degradation in ACD services. For example, Japanese Patent Application Laid-open Publication No. 8-51480 (1996) discloses a technique to ensure the successful hunting of data channels by previously reserving them for exclusive use, where the channel reservation process is performed by an electronic switching system located on the side of call originators. This proposed technique, however, is not based on a true negotiation between two switching systems concerned, and therefore, it does not guarantee the successful establishment of call connections, even if they are attempted with the reserved channels.
Further, in the above-described conventional system, the reserved data channels will be canceled once they are allocated to some subscribers. In other words, a reservation made for a specific subscriber is automatically terminated at the end of a subsequent call. As such, the conventional system does not allow any particular channel reservation to be maintained for a long time.
Still another problem with the conventional system is that the system is designed to reserve a predetermined number of data channels, but it does not provide flexibility in this area. When the predetermined number is too small, actual incoming calls may sometimes overwhelm the system""s capacity. When, in turn, the predetermined number is too large, the resultant excessive channel reservation will hamper the access from other ordinary subscribers, avoiding efficient use of the ISDN transmission lines 30. In actuality, the traffic loads in ACD services vary with time. However, the conventional system design does not take this nature of ACD services into consideration.
Taking the above into consideration, a first object of the present invention is to provide a system for reserving data channels in an appropriate manner to ensure the connection set-up operations in a telecommunications service feature which has to continually handle a number of incoming calls, as in ACD services.
A second object of the present invention is to provide an originator-side channel reservation controller which reserves data channels in an appropriate manner to ensure the connection set-up operations.
Further, a third object of the present invention is to provide a recipient-side channel reservation controller which reserves data channels in an appropriate manner to ensure the connection set-up operations.
Moreover, a fourth object of the present invention is to provide a method of reserving data channels in an appropriate manner to ensure the connection set-up operations.
To accomplish the first to third objects, according to the present invention, there is provided a system for controlling reservation of data channels to be used for automatic distribution of incoming calls. This system comprises an originator-side channel reservation controller and a recipient-side channel reservation controller. The originator-side channel reservation controller comprises the following elements:
a channel allocation unit which determines the number of data channels to be reserved for a specific group of subscribers who may use the data channels;
a reservation request transmission unit which makes a provisional reservation for as many data channels as determined by the channel allocation unit and transmits a reservation request message to request reservation of the data channels; and
an originator-side reservation unit which establishes the channel reservation on the side of call originators by securing the data channels for exclusive use by the specific group of subscribers, in response to a channel reservation acknowledgment message.
On the other hand, the recipient-side channel reservation controller comprises the following elements:
a recipient-side reservation unit which establishes the channel reservation on the side of call recipients by securing the data channels for exclusive use by the specific group of subscribers, in response to the reservation request message sent from the reservation request transmission unit; and
a channel reservation acknowledgment unit which transmits the channel reservation acknowledgment message to the originator-side reservation unit to report a result status of the channel reservation made by the recipient-side reservation unit.
To accomplish the fourth object, according to the present invention, there is provided a method of controlling reservation of data channels to be used for automatic distribution of incoming calls. This method comprises the following steps:
(a) determining the number of data channels to be reserved on the side of call originators to handle incoming calls from a specific group of subscribers;
(b) making a provisional reservation of as many data channels as determined in the step (a) and issuing a reservation request message to the side of call recipients;
(c) reserving the requested data channels on the side of call recipients for exclusive use by the specific group of subscribers, in response to the reservation request message;
(d) sending a result status message to inform the side of call originators about the data channels that have been reserved in the step (c);
(e) establishing the channel reservation on the side of call originators by securing the data channels for exclusive use by the specific group of subscribers, in response to the result status message received from the side of call recipients.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.